Fluid or gas bearings have recently been utilized in a large number of diverse applications. These fluid bearings generally comprise two relatively movable elements with a predetermined spacing therebetween. The spacing is filled with a fluid such as air, which, under dynamic conditions forms a supporting wedge to provide sufficient support for a load by preventing contact between the two relatively movable elements.
More recently, improved fluid bearings, particularly gas bearings of the hydrodynamic type, have been developed by providing foils in the space between the relatively rotatable bearing elements. Such foils, which are generally thin sheets of a compliant material, may be deflected by the hydrodynamic film forces between adjacent bearing surfaces and the foils. The foils enhance the hydrodynamic characteristics of the fluid bearings and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, foils provide the added advantage of accommodating eccentricity of the relatively movable elements and further provide a cushioning and dampening effect.
The ready availability of relatively clean process fluid air or ambient atmosphere as the bearing fluid makes these hydrodynamic, fluid film lubricated, bearings particularly attractive for high speed rotating machinery. While in many cases these hydrodynamic or self-acting fluid bearings provide sufficient load bearing capacity solely from the pressure generated in the fluid film by the relative motion of the two converging surfaces, it is sometimes necessary to externally pressurize the fluid between the bearing surfaces to increase the load carrying capacity. While these externally pressurized or hydrostatic fluid bearings do increase the load carrying capacity they do introduce the requirement for an external source of fluid under pressure.
A major disadvantage with both hydrodynamic and hydrostatic foil bearings, is that the load capacity does not increase indefinitely with speed but tends to level off or approach a fixed value. Thus, for a given load, these bearings are useful up to a given speed beyond which failure would be likely to occur. In addition, the distribution of fluid across the length of the bearing may be such as to create hot spots or the like.
Examples of hydrodynamic and/or hydrostatic bearings assigned to the Assignee of this application are U.S. Pat. Nos. 3,215,479, 3,215,480, 3,366,427, 3,375,046, 3,382,014, 3,434,761, 3,434,762, 3,467,451, 3,511,544, 3,560,064, 3,615,121, 3,635,534, 3,642,331, 3,677,612.